The present invention relates generally to antennas and more specifically the invention pertains to a phased array antenna feed system.
Large arrays are often treated as arrays of smaller subarrays for the purpose of simplifying the array control and reducing cost. Two major applications of subarray techniques are for limited field of view scanning and for time delay compensation of phase steered arrays.
Using space-fed overlapped subarray technique, it is possible to divide an array into subarrays and provide good performance for two applications that require subarrays. One application is for scanning over a limited field of view, where in the subarray is used to reduce the number of phase controls. A second application is to insert time delay at the subarray ports, while using phase shifters at the antenna elements.
Unfortunately, space fed systems have large volume, and so for many applications it is desirable to build arrays with fully constrained transmission line networks and power dividers. This can be done most simply using contiguous, uniformly illuminated subarrays, but that causes large sidelobes for both of these applications. Alternative partial overlapping techniques have been developed for constrained networks, and these have been useful for limited field of view scanning applications, but they are relatively complex to construct, and their sidelobe control is limited. These techniques are even more limited for the application of inserting time delay at the subarray ports of phase steered arrays, because this application implies use of very large subarrays, and these techniques are only suitable for overlapping a relatively small number of elements.
Current phased array feed systems are described in the following U.S. Patents, the disclosures of which are incorporated herein by reference:
U.S. Pat. No. 5,694,134, Dec. 2, 1997, PHASED ARRAY ANTENNA SYSTEM INCLUDING A COPLANAR WAVEGUIDE FEED ARRANGEMENT, Barnes, Frank;
U.S. Pat. No. 5,365,239, Nov. 15, 1994, FIBER OPTIC FEED AND PHASED ARRAY ANTENNA, Stilwell, Jr., P. Denzil;
U.S. Pat. No. 5,087,922, Feb. 11, 1992, MULTI-FREQUENCY BAND PHASED ARRAY ANTENNA USING COPLANAR DIPOLE ARRAY WITH MULTIPLE FEED PORTS, Tang, Raymond, Fullerton, Calif. Lee, Kuan M., Brea, California Chu, Ruey S.;
U.S. Pat. No. 4,757,318, Jul. 12, 1988, PHASED ARRAY ANTENNA FEED, Pulsifer, Paul I., Kanata, Canada Cornish, William D. Nepean, Canada Conway, Larry J.;
U.S. Pat. No. 4,566,013, Jan. 21, 1986, COUPLED AMPLIFIER MODULE FEED NETWORKS FOR PHASED ARRAY ANTENNAS, Steinberg, Richard;
U.S. Pat. No. 4,446,463, May 1, 1984, COAXIAL WAVEGUIDE COMMUTATION FEED NETWORK FOR USE WITH A SCANNING CIRCULAR PHASED ARRAY ANTENNA, Irzinski, Edward P.;
U.S. Pat. No. 4,394,660, Jul. 19, 1983, PHASED ARRAY FEED SYSTEM, Cohen, Leonard D.; and
U.S. Pat. No. 3,739,389, Jun. 12, 1973, DUAL FUNCTION FEED SYSTEM FOR PHASED-ARRAY RADAR, Bowman, David F.
To date, I know of no constrained feed technique that can provide good pattern control for large subarrays, particularly for large space fed systems.
Although effective subarraying can be readily implemented using space feeds, it has remained very difficult to produce good pattern control with constrained feeds. There is a need for several new solutions to the problem, as applied to one dimensional arrays. The extension to two-dimensional scanning can be accomplished by cascading the beamformer networks. It is expected that these techniques will enable the fabrication of low sidelobe arrays with very large constrained subarrays.
The invention is a procedure and associated hardware to enable a phased array to be fed from a number of subarray ports while maintaining good sidelobe control. The invention pertains to using constrained feed networks, like Rotman lenses, Butler matrices and waveguide networks instead of a single space feed, to produce these subarrays. The formed subarrays are partially overlapped, and this is required to develop good sidelobe control.
The invention solves the problem of having high sidelobes when an array is fed by contiguous, uniformly illuminated subarrays and so allows optical time delay, digital time delay and limited field of view scanning with a constrained network while maintaining low sidelobe radiation.
The object of the invention is to develop a new contrained feeding technique for limited field of view arrays and time delayed subarrays that has good sidelobe control. These applications are needed for space based radar systems, and a number of ground and airborne array systems for both radar and communication.
This object together with other objects, features and advantages of the invention will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings wherein like elements are given like reference numerals throughout.